On-vehicle brake disk lathes are employed to machine the surfaces of brake disks to maintain the brakes in proper working order. The on-vehicle lathe mounts to a wheel hub of the vehicle and allows the disk associated with that hub to be machined without requiring the disk to be removed from the vehicle on which it is mounted. Such lathes have a movable cutting head assembly which serves to position a pair of tool bits that machine the surfaces of the brake disk while the brake disk is rotated about a disk axis. The tool bits are each supported on an arm, and the arms in turn are adjustably mounted to a plate. Arm adjusting knobs mounted to the plate are functionally connected to the pair of arms to cause the arms to move in response to rotation of the knobs. The movement of the arms moves the tool bits in a direction that is substantially parallel to the disk axis, and the position of the tool bits determines the depth of the cuts on the disk surfaces when they are machined.
Since the on-vehicle lathe mounts to a wheel hub and the distance from the wheel hub to the brake disk differs for different vehicles, the plate on which the arms are mounted should be adjustable in a direction parallel to the disk axis to allow the tool bits to be positioned straddling the brake disk. The plate must also be movable in a direction normal to the disk axis, to allow the tool bits to be drawn across the disk surfaces during the machining procedure. These motions are achieved by employing a platform which is mounted on the lathe so as to be advanceable in a direction normal to the disk axis. In turn, the plate is adjustably mounted to the platform such that its position along the platform in a direction substantially parallel to the disk axis can be adjusted as desired.
One approach for adjusting the position of the plate on the platform is taught in U.S. Pat. No. 6,363,821, which teaches a plate with a keyway that is slidably engaged with a key protruding from the platform. The key and the keyway extend substantially parallel to the disk axis. A threaded shaft is rotatably mounted in the platform and threadably engages the plate such that rotation of the shaft causes the plate to slide along the key. The '821 patent teaches the use of a servo to rotate the threaded shaft. To allow sufficient rigidity in maintaining the position of the plate along the platform, the threading of the shaft would need to be relatively fine, as a coarse thread would allow any rotational freedom of the shaft to allow a substantial change in the axial position of the plate. The requirement that fine threads be employed means that repositioning the plate a substantial distance along the platform will require a large number of rotations of the shaft, slowing the adjustment. This approach also suffers in being mechanically complex, and does not appear to have been used commercially.
A simpler approach to adjusting the axial position of the plate on the platform, which has been commercially successful, is illustrated in FIG. 1. FIG. 1 illustrates a cutting head assembly 10 for machining a brake disk 12 that rotates about a disk axis 14. The cutting head assembly 10 employs a platform 16 that is provided with an overhanging inclined rear surface 18 that extends substantially parallel to the disk axis 14. The platform 16 also has a series of threaded holes 20 that are arranged in a line parallel to the overhanging inclined rear surface 18. A plate 22 has an inclined trailing edge 24, which is configured to engage against the overhanging inclined rear surface 18, and has a slot 26 which is oriented with its direction of elongation parallel to the inclined trailing edge 24. A securing bolt 28 passes through the slot 26 and secures into a desired one of the threaded holes 20. Tightening the securing bolt 28 acts to clamp the plate 22 to the platform 16.
The slot 26 has a slot length LS that is somewhat greater than the separation SH between adjacent threaded holes 20 to allow continuous adjustment of the position of the plate 22 along the platform 16. The slot is also oversized in width, having a slot width Ws which is greater than the diameter D of the securing bolt 28 that passes therethough, so as to allow the user to slide the inclined trailing edge 24 of the plate 22 into intimate contact with overhanging inclined rear surface 18 before tightening the securing bolt 28. If the desired position of the plate 22 is beyond the range allowed by the slot 26, the user removes the securing bolt 28 from the threaded hole 20 in which it currently resides and places the plate 22 in the desired position, aligning the inclined trailing edge 24 against the overhanging inclined rear surface 18. The securing bolt 28 is then passed through the slot 26 into whichever of the threaded holes 20 resides thereunder, and is tightened to secure the plate 22 in the new position on the platform 16.
While this system benefits in being mechanically simple, it is dependent on correct technique by the operator. To assure adequate stability during the cutting process, the operator must assure that the inclined trailing edge of the plate is firmly pressed against the overhanging inclined rear surface of the platform when tightening the stop bolt. If these surfaces are not tightly engaged, the plate will only be stabilized at the location where it is clamped to the platform by the stop bolt, which may not allow sufficient stability to assure accuracy in machining the brake disk surfaces. Furthermore, since the plate is loose from the platform once the stop bolt is removed, there is a risk of dropping the plate, particularly when the lathe is adjusted when in an inverted position. The need to manipulate separate pieces to adjust the position of the plate complicates the adjustment procedure, and may slow the machining process.